For many decades, land vehicles and also airplanes have been provided with wheels comprising a rim and a pneumatic tire mounted on the rim. Due to the rather high angular velocities of such wheels during use and the danger of rupture of the tire due to encounters with obstacles in its path, the casings of prior art tires almost uniformly have been provided with extensive reinforcements in the forms of fabrics or cords made from natural or synthetic materials or metal, or both.
In most early applications of such pneumatic tires, the tire comprised a reinforced carcass having a U-shaped cross-sectional configuration with annular beads which engaged the rim. A torus-shaped inner tube was positioned within the tire carcass in engagement with both the carcass and the outer diameter of the rim. In such wheels, which are still in extensive use, the rim and tire carcass provide the necessary mechanical strength and the tube provides the necessary airtight interior volume during operation. More recently, tubeless tires have come into general use in which the carcass of the tire is sealed directly to the rim to provide the airtight interior volume, thus eliminating any need for an inner tube.
To ensure adequate load bearing capacity, to retain such prior art tires on their rims and to ensure that such wheels can resist the torque applied to drive and brake such vehicles, the tire carcasses have typically been quite rigid and far less flexible than their inner tubes. Both tube type and tubeless tires have been inflated to a rather high operating pressure, typically well in excess of 25 pounds per square inch. When such prior art wheels are mounted on a vehicle and subjected to an axle load, the tire flattens very slightly and, in general, retains an exterior appearance quite similar to that of an uninflated, unloaded wheel.
Such prior art wheels are admirably suited for use on vehicles which operate over relatively hard, even support surfaces. However, should the vehicle encounter a soft surface such as beach sand or a rather irregular surface such as rocky terrain, then the performance of the prior art wheel often is less than satisfactory. Specifically, the contact area between the prior art tire and the underlying support surface is so small that the pressure per unit area is extremely high on the underlying support surface, which often causes the wheels of the vehicle to sink at least partially into soft support surfaces such as beach sand. On irregular surfaces, the relatively hard, unyielding nature of such prior art tire carcasses and their high inflation pressure make it difficult for the tire to yield to obstacles in its path so that the vehicle can go forward with a minimum of applied power. In some instances, large expensive wide track tires have been used in self-powered vehicles to facilitate their movement over soft and irregular surfaces due to the increased contact area of the wide track tire.
A variety of carriers or vehicles have been developed in recent years which are intended to be pulled over soft or irregular surfaces, usually manually but also by self-powered tractors. For example, U.S. Pat. No. 4,327,933 granted to W. E. Tuggle for "Sailboat Carrier" discloses a type of carrier suitable for moving catamaran sailboats across wide expanses of beach sand and into the water. While small wheels of the prior art type previously discussed can be used on such carriers, a still significant effort is required to move the loaded carrier across a beach. A need has continued to exist for a wheel having both a much larger contact surface to minimize sinking into soft surfaces and a more elastic and flexible tire body both to permit easy deformation of the tire as it rolls over obstacles in its path and to permit the contact area of the tire to increase very substantially under load.